1. Field of the Invention
The present invention relates the prophylactic use of a composition to reduce the incidence of contraction of illnesses caused by microbial organisms. More particularly, the present invention relates to methods for treating, reducing or preventing one or more symptoms or adverse effects of a microbial infection and to methods for reducing the infectivity or transmission of microbial infections.
2. Description of the Related Technology
Viral pathogenesis is the method by which viruses produce disease in the host. The pathogenesis of viruses centers on the mechanisms of viral injury to discrete populations of cells in particular organs to produce signs and symptoms of disease in a particular host.
To initiate an infection the virus must gain entry to the host cell. Entry routes are dependent on the virus and include the skin, eyes, respiratory, GI and urogenital tracts as well as the circulatory system. Some viruses localize their tissue injury in close proximity to their site of entry, particularly the viruses that infect the upper respiratory tract such as influenza, parainfluenza, rhinoviruses and coronavirus. Once the viral particle has invaded the cell, viral coded proteins direct the cell to replicate the viral genome and produce viral specific proteins. These proteins are assembled into complete virions along with the viral genome and released. In the case of enveloped viruses, the virions acquire a lipid membrane and will insert through this lipid membrane, viral specific glycoproteins. The enveloped virus families include the Herpesviridae, Retroviridae, Orthomyxoviridae, Paramyxoviridae, Flaviviridae, Togaviridae and Coronaviridae. The rhinoviruses are members of the Picornaviridae, which are not enveloped.
Viruses have evolved a number of mechanisms to enter a host cell and initiate infection. To fuse to the cell membrane, viruses have a membrane glycoprotein with membrane fusion activity. Many enveloped virus induce a receptor-mediated endocytosis after binding to the cell surface receptor, causing the cell to form an endosomal vesicle. Once inside the vesicle, the virus particle undergoes the uncoating process. This insures that the optimal pH for the viral genome is maintained and that the viral genome is protected from cellular nucleases.
Influenza viruses belong to the Orthomyxoviridae family of viruses and they are enveloped viruses containing negative-stranded RNA genomes with eight segments. The viral RNA encodes 10 viral specific proteins. Initiation of the infective cycle requires the binding of the viral envelop to the host cell-surface receptors, followed by receptor-mediated endocytosis and the fusion of the viral and endosomal membranes. The fusion process allows the release of the viral genome into the cytoplasm, where it can migrate to the nucleus where the viral genome initiates viral transcription and replication. The protein responsible for influenza receptor binding and membrane fusion is the hemagglutinin protein (HA or H antigen). For most strains, the HA protein is the most abundant glycoprotein on the surface of the virion. The HA protein is also the target for neutralizing antibodies. There are three serotypes of influenza viruses: A, B and C. Serotypes A and B cause the majority of clinical diseases. Influenza A occurs the most frequently, it is more virulent and it is responsible for the majority of epidemics and pandemics. Influenza A can be further subtyped based on the surface antigens HA and neuraminidase (N antigen) and the H and N antigens are the major antigenic determinants. Strains are also classified based on geographical location of the first isolate, serial number and year of isolation. Neuraminidase is an enzyme that facilitates the release of new viral particles from infected host cell. A third protein, M protein (matrix protein), is a membrane channel protein and is known as M2 in the A strains and NB in B strains. These surface viral membrane glycoproteins are the targets against which the immune system reacts.
Influenza viral particles attach to epithelial cells in the upper and lower respiratory track, where they invade the cell, release their genome and subjugate the host cell replication machinery to reproduce viral proteins and nucleic acid. Mature viral particles are released by lysis of the host cell. The resulting breaches in the respiratory epithelium results in an increase susceptibility to secondary infection. Influenza is transmitted primarily by respiratory secretions and these secretions are spread by coughing and sneezing. Influenza is also spread by direct contact when hands contaminated with the virus come in direct contact with the nasal passages or the eye. The incubation period is from 1 to 4 days and infected persons are generally infectious a day or two before symptoms appear and can remain infectious for 5 days after the onset of illness. Children and the immunocompromised shed virus for longer periods.
Influenza is prone to minor changes (i.e. point mutations) to one or both of the major surface antigens during replication. These changes are due in part to the lack of proofreading and error correction mechanisms in the virus transcriptional apparatus. The so-called antigenic drift is responsible for the seasonal epidemics because it can enable the virus to infect persons with only partial immunity from a prior exposure to the virus. Influenza A viruses are especially prone to antigenic drift. Major changes in the H and N antigens result in antigenic shift. Antigenic shift results in a new viral subtype and it can cause major epidemics and pandemics due to minimal populational immunity.
Influenza has been established as a serious human affliction that can cause localized epidemics and global pandemics of acute respiratory infections. Each year the influenza virus is responsible for 20,000 to 40,000 deaths and up to 300,000 hospitalization cases in the US. (Sandha and Mossad, Influenza in the Older Adult. Indications for the Use of Vaccine and Antiviral Therapy, Geriatrics 56:43-51, 2001, Oxford et al, In: Antigenic Variation, Ed. Craig & Scherf, Academic Press, London pp. 53-83, 2003). In the pandemic of 1918 it is widely believed that an excess of 40 million people died. Although children and younger adults experience more cases of infection, severe illness is more common in the elderly or immunocompromised individuals with chronic illnesses such as asthma, diabetes, kidney failure and heart disease. The annual epidemics run from November to March in the Northern Hemisphere and from April to September in the Southern Hemisphere.
Avian influenza is caused by type A strains of influenza virus. Avian influenza occurs throughout the world. Infected birds may display a wide range of symptoms, from a mild illness to a highly contagious fatal disease. The highly contagious disease is caused by an especially virulent strain of influenza virus. Infection by this strain is associated with a sudden onset of severe symptoms, such as a lack of energy, decreased egg production, soft shelled eggs, a swelling of the head, eyelids, etc., nasal discharge, coughing or diarrhea, resulting in death (WHO, 2004). At present, 15 subtypes have been identified that can infect birds but only H7, H5 and H9 subtypes are associated with outbreaks. The current Asian and British Columbia outbreaks are caused by a H5N1 and H7N3 strains, respectively. As discussed above, influenza viruses are a public health concern because these viruses lack a mechanism for proofreading nucleic acid replication as well as a repair system for correcting such errors. Thus, influenza viruses are especially prone to a high mutation rate during transcription. Additionally, influenza viruses are able to exchange or swap genetic material from other subtypes from different species, thus allowing subtypes to cross the species barrier that normally prevents the cross infection of species specific viruses from one species to another unrelated species. This species barrier normally prevents avian influenza virus strains from infecting humans, but occasionally new strains may have genetic material from both avian and human influenza virus strains. This exchange of genetic material occurs when there is a close proximity between humans and domestic poultry and swine. Swine may act as a reservoir for both human and avian strains. Thus swine act as a natural incubator for the emergence of new strains that can infect humans as well as avian species.
There are four antiviral drugs available in the US for the treatment of influenza: amantadine, rimatadine, zanamivir (Zanamivir (Relenza™) and Oseltamivir (Tamiflu™). Amantadine and rimatadine are effective only against influenza A. Amantadine, rimatadine and oseltamivir are approved for prophylaxis. Prophylaxis is indicated only for unvaccinated persons at high risk during an influenza outbreak. Antiviral agents have limited use due to poor tolerance and the occurrence of resistance. Presently, amantadine is the principal antiviral compound used against influenza infection, but its activity is restricted to influenza A viruses. The anti-neuraminidase inhibitors such as Zanamivir and Oseltamivir are a new class of antiviral agents licensed for use in the treatment of both influenza A and B infections (Carr et al., Influenza Virus Carrying Neuraminidase with Reduced Sensitivity to Oseltamiver Carboxylate has Altered Properties In Vitro and is Compromised for Infectivity and Replicative Ability In Vivo, Antiviral Res. 54:79-88, 2002). Therefore, the development of new and effective antiviral drugs against influenza A and B is of great clinical importance (Bamford, Neuraminidase Inhibitors as Potential Anti-Influenza Drugs, J. of Enzyme Inhibition, Review 10:1-16, 1995).
Influenza vaccines are generally used before the onset of the influenza season and they are typically given to the segment of population that is considered to be at high risk. Vaccines come in several forms and they aim at preventing or at least lessening the symptoms of disease. Vaccines are given prior to exposure of the virus to generate neutralizing antibodies against the strain that is most likely to cause wide spread epidemics or pandemics. However, vaccinations can be costly and stocks of the vaccine can be depleted quickly. Also, vaccines may not contain the causative viral component. In other words, vaccine production depends upon estimating which strain will emerge as the dominant strain. Thus in any given year, there is only a limited protection against the various influenza strains. Furthermore, the typical method of providing a vaccine via injection is unpleasant to many. Prophylaxis treatments on the other hand, are used to prevent infection or lessen the severity of the disease post-exposure to the virus. Oseltamivir™ as well as zanamivir or Relenza™ (Glaxo Wellcome, second generation antiviral) are neuraminidase inhibitors that block the release of mature viral particles and thus prevent the infection of neighboring cells. Neuraminidase inhibitors lesson the symptoms of influenza infection and short the duration of the disease. Prophylaxis must be given within a 48-hour window of the onset of symptoms to be effective and there is a risk of resistant strains emerging.
Severe acute respiratory syndrome (SARS) is the first major new infectious disease of the 21 st century. The first cases appeared in November of 2002 in Guangdong, China but it was only recognized as a new disease in March of 2003. The spread of the disease was accelerated by international air travel such that cases were reported in 22 countries. However, with modern communication technologies and a global collaborative effort the disease was contained within four months of being identified. The disease caused high morbidity and high mortality rates, with symptoms including a high fever, headache, myalgia and a dry cough. The mortality rate exceeded 60% in the over 60 age group (Peiris J S et al., 2003). SARS was identified as being caused by a new virus through various laboratory techniques involving virus propagation in tissue culture and electron microscopy studies. This was confirmed just days later when the complete genome sequence was determined indicating that it was a new Coronavirus that was responsible. Therefore the development of antimicrobial drugs for use against this type of infectious disease is of great importance.
Other microorganisms that cause illness include the gram-positive and gram-negative bacteria such as Streptococcus, Staphylococcus, E. coli, Pseudomonas, and Haemophilus as well as fungal infections including the yeast, C albicans. While active infection with these microorganisms is primarily treated with antibiotics, some patients do not tolerate antibiotics well. Still others may wish to augment an antibiotic treatment with a treatment regiment that reduces or eliminates the symptoms of bacterial or fungal infection such as sore throat. Still others may want to prevent or lessen the severity of infections by one of these bacteria or fungi organisms by prophylactic treatment prior to, during or just after exposure.
Research interest has recently focused on various herbs, which contain potent antioxidant compounds that can provide significant protection against chronic diseases and have antimicrobial or anti-tumour activity. Antioxidant substances such as flavonoids can be found in a variety of herbs such as dandelion, ginger, green tea, and rosemary. It was recently reported that green-tea extract (GTE) inhibited the growth of influenza A and B viruses in Madin-Darby canine kidney (MDCK) cells and in another study, Epigallocatechin-3-gallate (EGCG), one of the components of green tea, inhibited the replication of HIV-1 (111B) and Bal HIV strains in peripheral blood lymphocytes. These substances have proven useful in the field treating various illnesses; however there has not been any progress in the creation of a prophylactic method for use with antioxidant substances.
Therefore, there exists a need in the field to provide a prophylactic method for the reduction of the incidence of contracting an illness caused by a microbial organism.